150 Canadian Record of Science. 



artery which divides into anterior and posterior 

 branches, and supplies the whole body with blood. 

 The blood enters the ventricle from below through a 

 pair of auricles (partly communicating with each other) 

 which receives it from the gills. The blood is colour- 

 less, and there are no regular veins, the arteries opening 

 into irregular spaces amongst the organs. 



Beneath the body cavity on each side is situated the 

 kidney. This organ has the appearance of a mem- 

 branous sack — difficult to see except when a perfectly 

 fresh Oyster is examined under water, when one can 

 distinguish it by the yellowish green colour of its 

 contents. #t is then seen that it sends out a number 

 of branches radiating out over the surface of the liver. 

 The kidney has two openings, one leads into the body- 

 cavity, the other to the exterior underneath the 

 adductor. 



Radiating out over the surface of the liver and inter- 

 mingling to a certain extent with the branches of the 

 kidney are another series of tubes which, gradually 

 uniting with one another, form a duct which opens by 

 the same aperture as the kidney. These tubes are the 

 organs of sex, and at the period of sexual maturity they 

 assume a milky white colour owing to the colour of 

 their contents. In the European Oysters the same 

 tube produces in succession milt and spawn, and the 

 animals are therefore hermaphrodite ; but in the Oyster 

 that inhabits the Canadian and American coasts, the 

 sexes are separate, although it is almost impossible to 

 detect them by the naked eye. There is no difference 

 in colour, but there is a slight difference in the amount 

 of branching of the reproductive tubes, and after some 

 practice it becomes possible to be pretty certain about 

 the sex of an individual even before the test of the 

 microscope is applied. 



There is another most important difference between 

 the Canadian and the European Oysters. In the latter 

 the milt alone is discharged into the sea; the eggs are 

 retained within the folds of the gills of the parent and 

 there fertilized. The young Oyster undergoes the first 

 stages of its development there, and when cast forth 



